The present invention relates to methods of lining the internal surface of a pipe, particularly to methods of lining the internal surface of an existing underground gas pipe, a water pipe, etc. for the purpose of internal surface repair or rehabilitation.
There has been known a pipeline resin lining method as illustrated in FIG. 10, in which a necessary amount of resin A and a spherical lining pig 112 are introduced into an existing underground pipe 111 and are moved forward through the pipe, so that a resin lining layer M is formed on the internal surface of the pipe 111.
In detail, using equipments as illustrated in FIG. 10, a valve 126 is opened and an air blower 118 is switched on, so that a necessary amount of resin received in a resin tank 116 is injected into the underground pipe 111 through a resin supply hose 120 and an inlet pipe section 114. Then, the spherical lining pig 112 is inserted into the pipe 111 by temporarily detaching one end of the hose 120 from the inlet pipe section 114. Subsequently, by continually operating the air blower 118, a pressurized air is supplied into the pipe 111 behind the resin A and the lining pig 112 through the same path. In this way, the resin A and the lining pig 112 are driven through the pipe 111 along the entire length thereof, so that the resin lining layer M is formed on the internal surface of the pipe 111.
However, since there may be some uneven interior surfaces such as corrosion pits and surface scale buildup within an underground pipe 111, the resin A and lining pig 112 will move with a relatively large resistance, making it necessary to apply a much larger air pressure behind the resin A and lining pig 112 in the pipe 111. But, if a larger air pressure is applied, a problem such as resin blow-off will occur on the resin lining layer M which has just been formed on the internal surface of the pipe 111, particularly such resin blow-off often appears in a seriously corroded area involving corrosion pin holes.
On the other hand, if merely suction force (not shown) is used to force the resin A and the lining pig 112 through the pipe 111, and if such suction force is quite larger in order to overcome various moving resistance as described above, it will be difficult for the resin to fill the corrosion pits or pin holes on the pipe interior surface.
Moreover, the above-described method as shown in FIG. 10 fails to perform a resin lining treatment on an existing underground pipe having a branch pipe, as illustrated in FIGS. 11 and 12. Referring to FIGS. 11 and 12, since an existing pipe a involves a branch pipe b communicated with the pipe a, a part of lining resin c will flow into the branch pipe b, resulting a problem that a branching position is clogged by the resin, and hence making it impossible to supply gas or water from the pipe a to the pipe b upon the hardening of the resin.
In order to solve the problem shown in FIGS. 11 and 12, an air pressure substantially equal to that for pushing the resin c and lining pig d, is applied from an open end of the branch pipe b so as to prevent the resin c from enterring the branch pipe b. However, if a branch pipe b has a large diameter or if the resin c has a comparatively low viscosity, a pressure applied through the open end of the branch pipe b will cause an air way e in the invaded part of the resin c, as shown in FIG. 12. As a result, it will be difficult to completely prevent the resin c from enterring the branch pipe b.
In addition, the above-mentioned method proves to be ineffective to perform a resin lining treatment on an existing underground pipe involving a larger diameter portion. One method for lining a pipe involving a larger diameter portion is to use two pigs with a necessary amount of resin placed therebetween. The front pig is in a spherical shape made of a resilient material having a larger diameter than the pipe inner diameter. While the two pigs are being air-driven through the pipe with the resin carried therebetween, a resin lining layer is formed on the internal surface of the pipe, by means of the rear pig having a smaller diameter than the pipe inner diameter. However, when the front larger resilient pig enters a larger diameter portion, some residual air remaining in the inner corners of the larger diameter portion can not smoothly escape therefrom because of a tight contact between the pig surface and the interior surface of the larger diameter portion, resulting a problem that some parts of the interior surface of the large diameter portion are not coated with the resin.